Currently, the electrophotographic technology is widely applied for copying machines, laser beam printers (hereinafter, “LBP”), fax machines or the like because of its high-speed processability, high image quality and so on.
As an electrophotographic photoreceptor in the field of this electrophotographic technology, inorganic photoconductive substances such as selenium, selenium/tellurium alloys, selenium/arsenic alloys, cadmium sulfide or the like have mainly been used conventionally. However, from the viewpoint of its toxicity, safety, cost, productivity or the like, electrophotographic photoreceptors using organic photoconductive substances have been developed these days.
When the organic photoconductive substance is a low molecular-weight substance, it is a general practice to mix the organic photoconductive substance with a binder resin to form a coating film. As the binder resin, various thermoplastic resins and thermosetting resins such as polymethylmethacrylate, polystyrene, vinyl polymers such as polyvinyl chloride and copolymers thereof, polycarbonate, polyester, polysulfon, phenoxy resins, epoxy resins and silicone resins have been used.
The electrophotographic photoreceptor using said various binder resins can be formed into a thin film with ease by means of a cast film-forming method. Moreover, it is suitable for mass production and can be provided relatively at a low price.
Of these various resins, polycarbonate resins show relatively excellent characteristics and hence are used popularly. Among them, a polycarbonate resin produced from 1,1-bis(4-hydroxyphenyl)cyclohexane (hereinafter, “bisphenol Z”) is used as a binder resin which is excellent not only in compatibility with an organic photoconductive substance but also in solvent solubility and abrasion resistance (Patent Document 1).
In recent years, handling of electrophotographic photoreceptors overseas is progressing quickly. In these circumstances, electrophotographic photoreceptors would be exposed to unexpected service environment on occasion according to the situation of each country.
A binder resin using the polycarbonate resin produced from bisphenol Z is excellent in solvent solubility but then is poor in solvent resistance. Therefore, there was a case where the surface of an electrophotographic photoreceptor was contaminated and the copied image was deteriorated in a scene where contamination by a human body-derived substance from an operator was assumed such as a scene of treating an electrophotographic photoreceptor in the process of producing, a scene of installing an electrophotographic photoreceptor to a toner cassette and a scene of replacing a toner cassette wherein an electrophotographic photoreceptor was loaded.
In the meantime, in the process of producing an electrophotographic photoreceptor, the environmental problem refrains from use of halogenated hydrocarbon. Therefore, a solvent containing tetrahydrofuran (hereinafter, “THF”) which is a non-halogen solvent as a main component has become a mainstream and thus, dissolving to this solvent in a high concentration has become the essential qualification required for a binder resin. Patent Document 1: Jpn. Pat. Publication No. S60-172044